I have got my 3 pole isolator below my switch to the bathroom light outside of the room, i have run a 3 core and earth from the isolator to the fan and a link cable from the light switch to the isolator switch, could somebody please show me how to connect cables in the form of a simple diagram, the colour codes in my 3 core are black, grey and brown.

very unlikely you can make this work.
most switches only have a live in plus switch line out to light so no neutral at switch.
If only one twin & earth at switch then no can do.
Normally the supply to fan isolator comes from ceiling light where there is a Neutral, permanant live and switch line.
The colours to conform to recommendations should be:
Brn = Perm. live.
Blk = sw. Line (over sleeved brown)
Grey = Neutral (over sleeved Blue).
If you are fortunate that the feed to the light goes via the switch there will be a connector block in the box for the Neutrals, connect your blue sleeved grey to them.
Brown to live side of switch,
brown sleeved black to other side of switch.
I assume the fan is inline in loft type not fitted in bathroom ceiling as this would be 'Part-p' notifiable work as would connecting to bathroom light,
(just mention that to cover me).
always work on dead circuits.
Make sure live/line correct way round at fan as can blow timer board if swopped.
regards

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